In recent years, HSUPA (High Speed Uplink Packet Access) is being researched as a transmission standard for achieving high-speed for communication packets of an uplink in W-CDMA (Wideband-Code Division Multiple Access). In HSUPA, an E-DCH (Enhanced-Dedicated Channel) is provided as a dedicated channel for transmitting uplink packets.
The power of this E-DCH occupies portions of received signal power for the base station apparatus other than portions for thermal noise power, other cell interference power, and power of dedicated channels used in communication such as for speech etc. In other words, it is possible to allocate E-DCH to power where three types of power of thermal noise power, other cell interference power, and dedicated channel power are subtracted from the RoT threshold value (RoT (Rise over Thermal threshold)) indicating the maximum receiving power that can be received by a base station apparatus.
Here, it is necessary to allocate E-DCH power to mobile station apparatuses efficiently and to carry out uplink packet communication because a plurality of mobile station apparatus belong to the cells covered by the base station apparatus. Non patent document 1 discloses carrying out scheduling by base station apparatus in order to distribute this E-DCH power to the mobile station apparatus in an efficient manner.
On the other hand, the mobile station apparatus carries out a soft handover during positions near the boundary of a plurality of cells and communicates with a plurality of base station apparatuses. At this time, regarding the mobile station apparatus during soft handover, scheduling is carried out by a plurality of base station apparatuses, and the uplink transmission rate is controlled. Namely, transmission rate commands are transmitted from a plurality of base station apparatuses to one mobile station apparatus to control the uplink transmission rate, and the mobile station apparatus is required to decide the actual uplink transmission rate from the plurality of transmission rate commands.
One such transmission rate control method is proposed in, for example, non patent document 2. In non patent document 2, one primary cell is selected from cells of a plurality of base station apparatuses with which a mobile station apparatus communicates at the same time during a soft handover (hereinafter referred to as “active set” base station apparatuses). A primary cell base station apparatus freely instructs a transmission rate of the mobile station apparatus including transmitting an absolute transmission rate command (AG: Absolute Grants) specifically specifying an uplink transmission rate. A base station apparatus for non-primary cells other than the primary cells transmits a relative transmission rate command (RG: Relative Grants) indicating either of “HOLD” indicating maintaining of the transmission rate or “DOWN” indicating reduction in the transmission rate. The primary cell base station apparatus also transmits RG as the transmission rate command but the primary cell base station apparatus not only transmits “HOLD” and “DOWN” as the RG, but also transmits “UP” indicating to increase the transmission rate. Namely, the primary cell base station apparatus freely instructs the transmission rate using both AG and RG, and, in contrast, the non-primary cell base station apparatus instructs other than to increase the transmission rate using just RG.
Although the mobile station apparatus basically conforms to AG or RG from the primary cell, by taking into consideration RG from the non-primary cell, the mobile station apparatus is able to achieve prompt optimization of the transmission rate and suppress increase in interference power at all cells of the active set base station apparatuses.
Specifically, referring to FIG. 1, the case where cell of base station apparatus #1 of base station apparatuses #1 to #4 of the active set is a primary cell will be described. FIG. 1 is a view showing AG for the base station apparatus #1 (primary cell), RG for the base station apparatuses #2 to #4 (non-primary cell), the operations of the mobile station apparatus, and the transmission rate of the actual uplink.
For example, at time 1, base station apparatus #1 transmits an instruction (AG) indicating to carry out uplink communication at a transmission rate of 128 bps (kilobits per second) to the mobile station apparatus. Further, base station apparatuses #2 to #4 transmits “HOLD” (RG) indicating to maintain the current transmission rate to the mobile station apparatus taking into consideration propagation environment and communication conditions in the cells. In FIG. 1, holding of the transmission rate (HOLD) is shown by “H,” and reducing of the transmission rate (DOWN) is shown by “D.”
As the RG of base station apparatuses #2 to #4 are all “HOLD,” the mobile station apparatus determines that there are no non-primary cells where the interference power is excessive, sets the transmission rate to 128 kbps in accordance with the base station apparatus #1 and transmits packets.
Next, at time 2, base station apparatus #1 again transmits AG of 128 kbps. On the other hand, base station apparatus #2 transmits an instruction “DOWN” indicating to reduce transmission rate, and base station apparatuses #3 and #4 transmit “HOLD.”
As the RG of base station apparatus #2 is “DOWN,” the mobile station apparatus determines that the interferences power of a cell of base station apparatus #2 is excessive, and reduces the transmission rate by just a reduction width set in advance. The mobile station apparatus then reduces the transmission rate by one stage without conforming to AG of base station apparatus #1, sets 96 kbps, and transmits packets.
By carrying out this kind of transmission rate control, it is possible to rapidly change the transmission rate using AG of a primary cell, and suppress increases in interference power at non-primary cells using RG of non-primary cells.    Non patent document 1: 3GPP TR25.896 V6.0.0 (2004-03)    Non patent document 2: “EUL scheduling: signaling support,” 3GPP TSG-RAN WG1 Meeting #38bis, R1-041084 (2004-09)